1. Field of the Invention
This invention relates to polymer compounds and articles made from the compounds. More particularly, this invention relates to specific polyester blends useful in making heat-shrinkable films.
2. Background of the Invention
Heat-shrinkable or thermo-shrinkable films are well known and have found commercial acceptance in a variety of applications. Generally, at a given temperature, and particularly above the glass transition temperature (Tg), a thermoplastic film material will extend if subjected to tensile stress. If the extension is maintained while the temperature is sufficiently lowered below the glass transition temperature, a state of increased internal stress is set. However, the stress is relieved and the film contracts, i.e., shrinks, when the film is again heated to near the glass transition temperature or higher. If the plastic films are set by cooling after stretching in two directions, which are at right angles to each other, the film is capable of shrinking in both directions, i.e., biaxially stretched heat-shrinkable film is produced.
Heat-shrinkable plastic films are used as coverings, to hold objects together, and as an outer wrapping and labels for bottles, cans and other kinds of containers. For example, such films are used for covering the cap, neck, shoulder or bulge of bottles or for the entire bottles; for the purpose of labeling, tamper-evident protection, parceling, or increasing the value of the product; and for other reasons. In addition, such films may be used as a covering to package such objects as boxes, bottles, boards, rods, or notebooks together in groups, and such films may also be attached closely as a wrapping. The uses mentioned above take advantage of the shrinkability and the internal shrink stress of the film.
Shrink films can be classified into two categories as follows: (1) biaxially oriented film for over-wrapping wherein the film shrinks in both the x- and y-axis directions, and (2) uniaxially oriented sleeves which are widely used as tamper evident labels on food and pharmaceutical products and as primary labels on beverage bottles. This film primarily shrinks in the stretched or oriented direction and ideally has less than 5 to 10 percent shrinkage in the unstretched or nonoriented direction and desirably has no shrinkage in the unstretched or nonoriented direction. Usually these films are made into a tube shape, and after being wrapped around a bottle or around more than one pipe, for example, the film is shrunk by the application of heat so as to wrap or to parcel together the object or objects.
The materials used for the films mentioned above include poly(vinylchloride) (PVC), polystyrene, oriented polyethylene, oriented polypropylene, hydrochlorinated rubber, and polyesters. However, the aforementioned materials are not without their problems. For example, poly(vinyl chloride) generates chlorine gas when burned for disposal, and printing characters and graphics on polyethylene film is difficult.
Presently, PVC is the most widely used material due to its excellent shrink properties, good clarity and is low in cost. Ideally, polyester shrink films would have properties very similar to PVC films so that the polyester can serve as a xe2x80x9cdrop-inxe2x80x9d replacement on existing shrink tunnel equipment. PVC film properties that are desired for duplication include: (1) a relatively low onset temperature for shrinkage, (2) a total shrinkage which increases gradually and in a controlled manner with increasing temperature, (3) a low shrink force to prevent crushing of the underlying container, (4) a high total shrinkage (for example, 50 percent or greater) and (5) an inherent film toughness so as to prevent unnecessary tearing and splitting of the film prior to and after shrinkage.
Accordingly, it is desirable to prepare a polyester heat-shrinkable film that has similar shrink properties as PVC but without the environmental problems described above.
U.S. Pat. No. 5,859,116 issued to Shih on Jan. 12, 1999 discloses a heat-shrinkable film comprising a copolyester blend having 1 to 98.5 weight. percent of a PETG copolyester containing at least 95 mole percent terephthalic acid, 65 to 80 mole percent ethylene glycol and 35 to 20 mole percent CHDM; 98.5 to 1 weight. percent of a PET copolyester containing at least 75 mole percent terephthalic acid, 50 to 90 mole percent ethylene glycol and 50 to 10 mole percent diethylene glycol; and, optionally, 5 to 15 weight. percent of a crystallizable polyester such as PET.
U.S. Pat. No. 4,963,418 issued to Isaka et al. on Oct. 16, 1990 discloses a polyester heat-shrinkable film having a shrink ratio in the first axis of not less than 30 percent at 80xc2x0 C. and not less than 50 percent at 100xc2x0 C. and a shrink ratio in the perpendicular axis to the first axis of not more than 15 percent at a temperature of from 55-105xc2x0 C. The polyester components of the film all have glass transition temperatures above 95xc2x0 F. (35xc2x0 C.).
U.S. Pat. No. 3,187,075 issued to Seifried et al. on Jun. 1, 1965 discloses a method for making plastic films which, when heated at temperatures less than 100xc2x0 C., will shrink at least 30 percent in both directions.
U.S. Pat. No. 4,814,426 issued to Utsumi et al. on Mar. 21, 1989 discloses a heat-shrinkable polyester film having 100 to 30 parts by weight of a crystalline polyester (A), in which 70 to 100 mole percent of the dicarboxylic acid residue moiety is terephthalic acid and 50 to 100 mole percent of the glycol residue moiety is 1,4-cyclohexanedimethanol, having a heat of crystalline melting of not less than 3 cal/g and a melting point in the range of 200xc2x0 to 310xc2x0 C. and 0 to 70 parts by weight of a polyester (B) comprising terephthalic acid and/or 2,6-naphthalene dicarboxylic acid as the dicarboxylic acid residue moiety and ethylene glycol and/or 1,4-butadiene glycol as the glycol residue moiety. The polyester film has a ratio of shrinkage in the range of 40 to 90 percent in either of the longitudinal and transverse directions after 5-minute heat treatment at 100xc2x0 C., the ratio of shrinkage or expansion is not more than 15 percent in the other direction after 5-minute heat treatment at 100xc2x0 C. and a haze of not more than 10 percent at a thickness of 35 microns.
U.S. Pat. No. 5,985,387 issued to Mori et al. on Nov. 16, 1999 discloses a heat-shrinkable polyester film wherein the thermal shrinkage ratio in a main shrinking direction is about 20 percent or more after being treated in water of about 70xc2x0 C. for about 5 seconds, about 35 to about 55 percent after treated in water of about 75xc2x0 C. for about 5 seconds, and about 50 to about 60 percent after being treated in water of about 80xc2x0 C. for about 5 seconds, and after the film is shrunk by about 5 percent by treatment in water of about 75xc2x0 C. for about 10 seconds, the probability of the elongation at rupture of the film in the direction perpendicular to the main shrinking direction being about 20 percent or less, is about 10 percent or less.
U.S. Pat. No. 5,580,911 issued to Buchanan et al. on Dec. 3, 1996 discloses binary blends of cellulose esters and aliphatic-aromatic copolyesters, binary blends of cellulose esters and aliphatic polyesters, and ternary blends of cellulose esters and/or aliphatic polyesters and/or aliphatic-aromatic copolyesters and/or polymeric compounds.
Accordingly, there is a need for a polyester heat-shrinkable film having a relatively low onset temperature for shrinkage, which has an inherent film toughness so as to prevent unnecessary tearing and splitting of the film prior to and after shrinkage.
Briefly, the present invention is for a compositional blend of a polyester and an aliphatic-aromatic copolyester and a heat-shrinkable film made from the blend. The blend includes
(A) from about 50 to about 99 weight percent a polyester comprising:
(1) an acid residue moiety comprising from about 60 to 100 mole percent terephthalic acid and from 0 to about 40 mole percent of a second acid selected from the group consisting of isophthalic acid, adipic acid, azelaic acid, naphthalenedicarboxylic acid, succinic acid, cyclohexanedicarboxylic acid; and mixtures thereof; and
(2) a diol residue moiety comprising from about:
i. 0-50 mole percent diethylene glycol;
ii. 0-100 mole percent 1,4-cyclohexanedimethanol;
iii. 0-50 mole percent neopentyl glycol;
iv. 0-50 mole percent propanediol;
v. 0-100 mole percent 1,4-butanediol; and
vi. remaining mole percent is ethylene glycol; and
(B) from about 1 to about 50 weight percent of an essentially, linear, random aliphatic-aromatic copolyester or branched and/or chain extended copolyester thereof and having an inherent viscosity of about 0.2 to about 2.0 deciliters/gram as measured at a temperature of 25xc2x0 C. for a 0.5 g sample in 100 ml of a 60/40 parts by weight solution of phenol/tetrachloroethane and having repeating units of: 
xe2x80x83wherein
R1 is selected from one or more of the groups consisting of C2-C8 alkylene or oxylalkylene, and the mole percent of R1 is from about 80 to 100;
R3 is selected from one or more of the groups consisting of C2-C8 alkylene or oxylalkylene; C2-C8 alkylene or oxylalkylene substituted with one to four substituents independently selected from the group consisting of halo, C6-C10 aryl, and C1-C4 alkoxy; C5-C12 cycloalkylene (for example, 1,4-cyclohexanedimethanol); C5-C12 cycloalkylene substituted with one to four substituents independently selected from the group consisting of halo, C6-C10 aryl, and C1-C4 alkoxy; and the mole percent of R3 is from 0 to about 20;
R2 is selected from one or more of the groups consisting of C2-C12 alkylene or oxyalkylene; C2-C12 alkylene or oxylalkylene substituted with one to four substituents independently selected from the group consisting of halo, C6-C10 aryl, and C1-C4 alkoxy; C5-C10 cycloalkylene; C5-C10 cycloalkylene substituted with one to four substituents independently selected from the group consisting of halo, C6-C10 aryl, and C1-C4 alkoxy; and the mole percent of R2 is from about 35 to about 95;
R4 is selected from one or more of the groups consisting of C6-C10 aryl; C6-C10 aryl substituted with one to four substituents independently selected from the group consisting of halo, C6-C10 aryl, and C1-C4 alkoxy; C5-C10 cycloalkylene; C5-C10 cycloalkylene substituted with one to four substituents independently selected from the group consisting of halo, C6-C10 aryl, and C1-C4 alkoxy; and the mole percent of R4 is from about 5 to about 65;
wherein the weight percentages are based on the total weight of components (A) and (B);
the mole percentages of component (A) are based on 100 mole percent of the acid residue moiety and 100 mole percent of the diol residue moiety; and for component (B) the sum of the mole percent for R1 and R3 is 100 and the sum of the mole percent for R2 and R4 is 100.
Surprisingly, the compositional blends of the polyester and the aliphatic-aromatic copolyester of the present invention exhibit a greater percent shrink at temperatures below about 70xc2x0 C. than known polyesters or polyester blends used for heat-shrinkable films. Moreover, including the aforementioned weight percent of component (B), i.e., the aliphatic-aromatic copolyester, unexpectedly increased the ductility of the film so that a higher percentage of diethylene glycol (DEG) could be incorporated into a heat-shrinkable film and retain acceptable tensile and shrink properties.